Method of making corrugated tubing



Sept. 4, 1945. TRlTT 2,384,055

METHOD OF MAKING CORRUGATED TUBING Filed March 19, 1941 fizz-r572? Patented Sept. 4, ,1945

METHOD OF MAKING CORRUGATED TUBING Forest G. Tritt, Sherman, Ohio, assignor to The B. F. Goodrich Company, New York,

corporation of New York N. Y., a

Application March 19,1941, Serial No. 384,124

9 Claims. (Cl. 18-56) This invention relates to the manufacture of corrugated tubing of rubber or similar material,

such as the corrugated flexible tubing used for breathing tubes in gas mask assemblies. Such tubi customarily is made of rubber or similar flexible material and has relatively thin walls, the necessary resistance to collapse being obtained by molding the walls with a series of circumferential corrugations arranged in closely spaced relation. In longitudinal cross section the wall of such a tube has a generally sinuous outline in the corrugated zone. Such corrugated tubing has been made heretofore by conventional molding processes. Attempts have been made to utilize dipping methods in producing corrugated tubing but such attempts have met with failure principally because of difficulty in obtaining uniform wall thicknesses and uniformly sinuous corrugations due to the tendency of liquid rubber compositions to bridge over and close the closely spaced corrugations. The present invention aims to provide a simple, economical, and efficient procedure for manufacturing corrugated tubing directly from liquid rubber compositions by means of dipping processes without the disadvantages and difficulties which have been encountered in prior efforts. The invention may be readily understood from the following detailed description of a preferred embodiment as illustrated in the accompanying drawing.

Of the drawing:

Fig. l is a sectional elevation illustrating an early step in the manufacturing process and showing a deposition form immersed in a liquid rubber composition with a deposit of rubber on the form;

Fig. 2 is a sectional elevation showing the form of Fig. 1 together with the rubber deposit suspended in an oven for preliminary drying'of the deposit;

Fig. 3 is an elevational view illustrating the step of removing the rubber deposit from the deposition form;

Fig. 4 is an elevational view showing the rubber Y deposit after it has been transferred to a drying mandrel for further drying.

Fig. 5 is a sectional elevation showing the same rubber deposit after it has been transferred to a final shaping mandrel, the shaping mandrel together with the rubber deposit being suspended in a vulcanizing chamber.

Fig. 6 is a vertical section taken on line 6-6 of Fig. 5.

Fig. 7 is an elevational view showing a finished section of corrugated tubing made in accordance with the present invention, a portion of the tube being broken away and sectioned for clarity of illustration In manu. rcturing corrugated tubing according to the preferred embodiment of the invention i1- lustrated in the drawing, I first provide a deposition form H) which may be made of any suitable non-corr'odible material such asaluminum, glass, porcelain, wood or the like. The deposition form 10 ordinarily will consist of a cylindrical member provided through a major portion of its'length with circumferential ridges I l-I I adapted to form corrugations in the tubing. The ridges ll-i I correspond generally to the corrugated configuration desired in the tubing but the ridges are spaced more widely than the desired spacing of corrugations in the finished tubing, the conlI--H is essential to the invention so .long as the spacing is great enough to permit deposition'of thedesired thickness of rubber on the form without bridging across between the ridges. Obvi-- ously such spacing will vary with the. thickness of rubber being deposited and must be determined in each particular case. In the case of rubber deposits having a final, dried thickness of about 3& inch as hereinafter described, corresponding portions of adjacent ridges on the dipping form should be separated by a distance inch.

The deposition form I0 is immersed in a liquid rubber composition I 2 (Fig. 1) and a coating .deposit of unvulcanized rubber i3 is produced on the form by any common method. Preferably however. the liquid rubber composition should be a suitably compounded aqueous dispersion of rubber such as a compounded natural rubber latex. Also, the deposition of the rubber from such latex preferably should be accomplished with the aid of a coagulant preliminarily applied to the form as described in U. S. P. No. 1,908,719, the coagulant preferably but not necessarily having associated with it a finely divided powdery material to prevent blemishes and assist in stripping the rubber from the form as described in U. S. P. 'No. 1.924.214. The initial deposit of latex rubber on the form ordinarily will have about twice the thickness of the final dried deposit due to the presence of water in the initial deposit. Breathing tubes for gas masks customarily have a wall thickness of about 3.432 inch so that an initial latex rubber deposit for such tubing should be about 1 inch thick in the wet or undried state. It is this relatively great initial thickness of the deposit which makes it impossible to utilize a deposition form having closely spaced corrugation forming ridges correspondingto the desired final spacing of the corrugations.

The deposition form IO together with the rubber deposit I3 is next placed in any conventional drying means such as the oven l4 illustrated diagrammatically in the drawing (Fig. 2) and the rubber is preliminarily dried at least to an exof the order of tent sufficient to permit-handling of the deposit without unduly distorting it. Ordinarily, drying from 4 to 5 hours in hot air at 140 F. will sufiice. Alternatively, drying for 12 hours at room temperature will be satisfactory. After such drying, and preferably before the rubber deposit is completely dried, the deposit isfstripped from the dipping form in the usual manner. Such stripping may be facilitated by introducing compressed air between the deposit and the form as illustrated in Fig. 3. surround the deposit with a cylindrical guard spaced only slightly therefrom to limit the inflation of the deposit. The closed end of the deposit may be trimmed off at any convenient stage before or after the deposit is stripped from the form. V

After the partially dried deposit is removed from the dipping form, it is transferred to a drying mandrel I5 (Fig. 4) which preferably has a smooth cylindrical surface corresponding in diameter to the inner diameter of the tubing The deposit is then contracted lengthwise on the drying mandrel to bring the corrugations into more closely spaced relation and preferably to bring them into closer relation thanis desired in the finished tubing. While the deposit is maintained with the corrugations in such closely spaced relation, the deposit is further dried preferably until 'it is substantially completely dry. Usually, additional drying at this stage for 24 hours in hot air at 140 F. will be adequate.

The completely dried deposit I3 next is transferred to a shaping mandrel l6 (Figs. 5 and 6). The shaping mandrel 16 preferably comprises a cylindrical member having a diameter corresponding to the inner diameter of the tubing. The shaping mandrel I6 is provided with a series of spaced apart circumferential grooves H741 having gently curved bottoms corresponding to the curvature desired in the valleys of the corrugations in the tubing. Also the grooves ll|1 are spacedapart in accordance with the spacin desiredin the finished tubing; i. e., the grooves are spaced closer than were the corrugation forming .A-idges H on the deposition form 10. The grooves ll-I'l are separated by upstanding circumferential ridges l8l 8 which preferably project only slightly above the normal surface of the mandrel l6 and accordingly do not fill the corresponding corrugations in the rubber deposit placed thereover as the corrugations are relatively higher than the ridges. a shallow venting groove I9 extending generally lengthwise of the form across the circumferential grooves and ridges for the purpose of venting air and gases during the vulcanization hereinafter described.

As above indicated, the contracted and'dried rubber deposit (Fig. 4) is transferred to the shaping mandrel l6 where it is disposed in substantially the desired final configuration with the valleys of the corrugations associated with the grooves in the mandrel (Fig. 5). However, since the spacing of the grooves ll--ll is greater than was the spacing of the corrugations. during the preceding drying step, such disposition of the rubber deposit on the shaping mandrel will require some extension of the deposit lengthwise. This has been found to be highly desirable in providing a high degree of uniformity in the finished product. The shaping mandrel I6 with the rubber deposit properly disposed thereon is then placed in any conventional vulcanizing equipment, such as the conventional heating chamber It will also usually be desirable to fix It will usually be desirable to provide 20 diagrammatically illustrated in the drawing (Fig. 5) and the rubber is vulcanized by heating in the usual manner. The duration of the heating, of course, will vary depending upon the particular composition of the .rubber.

The final vulcanization of the rubber on the shaping form serves to set the rubber permanently in the desired final, form. If vulcanized latex is used, such final setting of course will be effected by the drying step and no vulcanizing step will be required. The vulcanized or otherwise finally set rubber deposit is then stripped from the shaping mandrel to produce the finished corrugated rubber tubing as illustrated in Fig. '7.

The present invention for the first time enables the rubber manufacturer to produce highly uniform and satisfactory corrugated rubber tubing with closely spaced corrugations by means of dipping processes. It is accordingly possible to attain all the economies of dipping processes without sacrificing uniformity in the product.

The term rubber has been used throughout the specification and claims in a generic sense to include all natural and synthetic rubbers and rubber-like materials having the pertinent characteristics of natural rubber including flexibility, extensibility and capability of utilization in liquid form in dipping processes.

having closely spaced circumferential corrugations, which comprises providing a deposition form having the general configuration of the desired tubing but having corrugation-forming ridges spaced more widely than the desired spacing of corrugations in the finished tubing, immersing the deposition form in a liquid rubber composition and producing a correspondingly corrugated deposit of unvulcanized rubberthereon, drying the deposit toa partial extent sufiicient. at least to permit handling, transferring the partially dried deposit to a substantially smooth drying mandrel, contracting the deposit longitudinally on the drying mandrel and thereby bringing the corrugations into closer spaced relation than desired in the finished tubing, further drying the deposit in such contracted condition on the drying mandrel, transferring the thus-dried deposit to a final shaping mandrel provided with circumferential grooves spaced apart in accordance with the spacing of corrugations desired in the 'finishing tubing, said spacing being intermediate between the spacing on the deposition form and the spacing during drying on the drying mandrel, disposing the deposit on the shaping mandrel in substantially the desired final configuration with the corrugation valleys of the deposit associated with the said grooves, and vulcanizing the rubber while the deposit is so disposed on the shaping mandrel.

2. The method of making corrugated tubing having closely spaced circumferential corrugations, which comprises providing a deposition form having the general configuration of the desired tubing but having corrugation-forming ridges spaced more widely than" the desired spacing of corrugations in the finished tubing, immersing the deposition form in a liquid rubber composition and producing a correspondingly corrugated deposit of unvulcanized rubber thereon.

drying the deposit to a partial extent sufficient at least to permit handling, transferring the partially dried deposit to a substantially smooth drying mandreLcontracting the deposit longitudinally on the drying mandrel and thereby bringing the corrugations into closer spaced relation than desired in the finished tubing, further drying the deposit in such contracted condition on the drying mandrel, transferring the thus-dried deposit to a .final shaping mandrel, disposing the deposit on the shaping mandrel in substantially the desired final configuration with thecorrugations extended rugated deposit of unvulcanized rubber thereon,

transferring the deposit to a substantially smooth drying mandrel, contracting the deposit longitudinally on the drying mandrel and thereby bringing the corrugations into closer spaced relation, drying the deposit to a substantial extent in such contracted condition, transferring the thus-dried deposit to a final shaping mandrel, disposing the deposit on the shaping mandrel in substantially the desired final configuration, and vulcanizing the rubber while the deposit is so disposed on the shaping mandrel.

4. The method of making corrugated tubing having closely spaced circumferential corrugations, which comprises providing a deposition form having the general configuration of the desired tubing but having corrugation-forming ridges spaced more widely than the spacing of cor- :rugations desired in the finished tubing, im- 1 mersing the deposition form in a liquid rubber composition and producing a correspondingly cor- .rugated deposit of unvulcanized rubber thereon,

transferring the deposit to a drying mandrel, drying the deposit to a substantial extent while on the drying mandrel, transferring the so-dried deposit to a final shaping mandrel, disposing the tions, which comprises providing a deposition form having the general configuration of the desired tubing but having corrugation-forming ridges spaced more widely than the desired spacing of corrugations in the finishing tubing, immersing the deposition form in a liquid rubber composition and producing a correspondingly corrugated deposit of unvulcanized rubber thereon, drying the deposit to a substantial extent, transferring the deposit to a shaping mandrel, disposing the deposit on the mandrel in substantially the-desired final configuration with the corrugations spaced more closely than on the deposition form, and vulcanizing the rubber while the deposit is so disposed on the shaping mandrel.

6. The method of making corrugated tubin having closely spaced circumferential corrugations, which comprises providing a deposition form having the general configuration of the desired tubing but having corrugation-forming ridges spaced more widely than the desired spacing of corrugations in the finished tubing, immersing the deposition form in a liquid rubber composition and producing a correspondingly corrugated deposit of unvulcanized rubber there on, drying the deposit to a substantial extent, transferring the so-dried deposit to, a shaping mandrel provided with circumferential grooves spaced more closely than the ridges on the deposition form and in accordance with the spacing of corrugations desired in the finished tubing, disposing the deposit on the mandrel in substantially the desired final configuration with the corrugation valleys of the deposit associated with the said grooves, and vulcanizing the rubber while the deposit is so disposed on the shaping mandrel.

7. The method of making corrugated tubing having closely paced circumferential corrugations, which comprises producing a corrugated tube of undried, unvulcanized rubber having the corrugations spaced more widely than desired in the finished tubing, contracting the tube longitudinally and thereby bringing the corrugations into closer spaced relation than desired in the finished tubing, drying the rubber to a substantial extent while so disposed in a -contracted condition, extending the so-dried rubber tube to bring the corrugations into thedesired spaced relation, and vulcanizing the rubber while maintaining the corrugations in the desired spaced relation.

8. The method of making corrugated tubing, which comprises providing a. deposition form having the general configuration of the desired tubing but having corrugation-forming ridges spaced more widely than the desired spacing of corrugations in the finished tubing, immersing the deposition form in a liquid rubber co mposition and producing a correspondingly corrugated deposit of rubber thereon, transferring the deposit to a shaping mandrel rovided with circumferential grooves spaced more closely than the ridges on the deposition form and in accordance with the spacing of corrugations desired in the finished tubing, disposing the deposit on the mandrel in substantially the desired final configuration with the corrugation valleys of the deposit associated with the said grooves, and vulcanizing the rubber while the deposit is so disposed on the shaping mandrel.

9. The method of making corrugated tubing, which comprises providing a deposition form having the general configuration of the desired tubing but having externally projecting corrugation-forming ridges spaced more widely than the desired spacing of corrugations in the finished tubing, associating the deposition form with a liquid rubber composition and producing on the external surface thereof a correspondingly corrugated deposit of rubber, transferring the deposit to a shaping mandrel provided with circumferential grooves spaced more closely than the ridges on the deposition form and in accordance with the spacing of corrugations desired in the finished tubing, disposing the deposit on the mandrel in substantially the desired final configuration with the corrugation valleys of the deposit associated with the said grooves, and setting the rubber to cause it permanently to retain,

such final configuration.

FOREST G. 'I'RI'I'I. 

